Multi-part capillary

ABSTRACT

A bonding tool for bonding a wire to a substrate. The bonding tool has a cylindrical body portion formed from a first material and a conical tip portion separately formed from a second material. The conical tip portion is coupled to one end of the body portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 60/526,896, filed on Dec. 4, 2003, the contentsof which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to a bonding tools used for fine wirebonding, and more particularly to a capillary bonding tool formed frommultiple and different materials.

BACKGROUND OF THE INVENTION

Modern electronic equipment relies heavily on printed circuit boards onwhich semiconductor chips, or integrated circuits (ICs), are mounted.The mechanical and electrical connections between the chip and thesubstrate have posed challenges for chip designers. Three well knowntechniques for interconnecting the IC to the substrate are: wirebonding, tape automated bonding (TAB) and flip-chip.

The most common of these processes is wire bonding. In wire bonding, aplurality of bonding pads are located in a pattern on the top surface ofthe substrate, with the chip mounted in the center of the pattern ofbonding pads, and the top surface of the chip facing away from the topsurface of the substrate. Fine wires (which may be aluminum copper orgold wires) are connected between the contacts on the top surface of thechip and the contacts on the top surface of the substrate. Particularly,the connecting wires are supplied and bonded to the chip and to thesubstrate through a capillary, a bonding tool further described below.

Capillaries (bonding tools) are used for ball bonding the wire toelectronic devices, particularly to bond pads of semiconductor devices.Such capillaries are generally formed from a ceramic material,principally aluminum oxide, tungsten carbide, titanium carbide, cermets,ruby, zircon toughened alumina (ZTA), alumina toughened zircon (ATZ).Very thin wire, generally on the order of about one mil gold, copper oraluminum wire, is threaded through an axial passage in the capillarywith a small ball being formed at the end of the wire, the ball beingdisposed external of the capillary tip. The initial object is to bondthe ball to a pad on the semiconductor device and then to bond a portionfarther along the wire to a lead frame or the like. During the bondingcycle, the capillaries perform more than one function.

After the ball is formed, the capillary must first center the ballpartly within the capillary for bond pad targeting. With a first bondingstep, the ball is bonded to a pad on a semiconductor device. When thecapillary touches the ball down on the bond pad, the ball will besquashed and flatten out. As the bond pads are generally made fromaluminum, a thin oxide forms on the surface of the bond pad. In order toform a proper bond, it is preferable to break the oxide surface andexpose the aluminum surface. An effective way of breaking the oxide isto “scrub” the surface of the oxide with the wire ball. The wire ball isplaced on the surface of the aluminum oxide and the capillary rapidlymoves in a linear direction based on the expansion and contraction of apiezo-electric element placed within the ultrasonic horn to which thecapillary is attached. The rapid motion, in addition to heat appliedthrough the bond pad, forms an effective bond by transferring moleculesbetween the wire and the bond pad.

The capillary then handles the wire during looping, smoothly feeding thebond wire both out of the capillary and then back into the capillary.The capillary then forms a “stitch” bond and a “tack” or “tail” bond.

Presently, thermosonic wire bonding is the process of choice for theinterconnection of semiconductor devices to their supporting substrates.The thermosonic bonding process is partially dependent upon the transferof ultrasonic energy from the transducer, attached to a movablebondhead, through a tool, e.g. capillary or wedge, to the ball or wirebeing welded to the semiconductor device or supporting substrate.

FIG. 1 is an illustration of a well-known prior art fine pitch bondingtool 100. As shown in FIG. 1, bonding tool 100 is formed from a unitarypiece of material having a cylindrical portion 101, a tapered portion102 coupled between cylindrical portion 101, and working tip 104. Tomeet the requirement of electrical isolation between the bonding machineand the device being fabricated, the material used to form bonding tool100 is non-conductive. Typically, this non-conductive material is abrittle ceramic based compound such as alumina, for example.

U.S. Pat. Nos. 5,871,141, 5,558,270, and 5,421,503 assigned to the sameassignee as the present invention, describe various conventional bondingtools for producing wire bonds on semiconductor devices and areincorporated herein by reference.

Conventional bonding tools are formed from non-conductive materials,such as alumina, and include a working tip used to form the bondsbetween the contact pad and the bonding wire. Such non-conductivebonding tools are necessary in order to protect the substrate beingbonded from potential electrical discharges from the bonding machine.Conventional bonding tools are deficient, however, because the ceramicmaterials from which they are formed are brittle and do not lendthemselves to be fabricated with working tip features that allow them toform bonds in ultra fine pitch applications so as to provide a highlevel of inter metallic coverage between the bonding ball formed by thetool and the bonding pad. Furthermore, conventional bonding tools areformed as a unitary part. It use, however, only the working tip of thecapillary becomes worn, but requires the replacement of the entire part,thereby wasting valuable material. Further, it is more difficult tomanufacture such a unitary bonding tool. For ease of manufacturingand/or replacement purposes, it would advantageous to provide a bondingtool where the working tip is separate from the shaft.

The inventors of the present invention have developed a bonding toolthat meets the demands imposed by these high-density devices whilemaintaining structural integrity of the bonding tool.

SUMMARY OF THE INVENTION

In view of the shortcomings of the prior art, the present inventionrelates to a bonding tool having a body portion formed from a firstnon-conductive material; and a working tip formed from a second materialhaving a conductive property, a first end of the working tip coupled toone end of the body portion.

According to another aspect of the present invention, the face of theworking tip has a circular profile, a square profile, or a rectangularprofile.

According to yet another aspect of the present invention, a working tipof a bonding tool for use with a bonding machine is provided. Theworking tip comprises an orifice extending in a longitudinal directionalong a central portion of the working tip; an inner chamfer coupled toan end of the orifice, the inner chamfer having a substantially arcuateprofile; and a exterior planar portion coupled to an end of the innerchamfer.

According to yet a further aspect of the present invention, the workingtip comprises an orifice extending in a longitudinal direction along acentral portion of the working tip; a plurality of substantially planarfaces formed at an inner portion of the working tip to form an innerchamfer having a polygonal shape; and a exterior planar portion coupledto respective ends of each of plurality of substantially planar faces.

According to still another aspect of the present invention, the workingtip comprise, an orifice extending in a longitudinal direction along acentral portion of the working tip; an inner chamfer having a first endcoupled to an end of the orifice; a exterior planar portion having afirst end coupled to a second end of the inner chamfer; and a furtherexterior portion coupled to a second end of the exterior planar portion,the further exterior portion disposed coaxially with the orifice andhaving a portion with a concave profile extending from the exteriorplanar portion.

The present invention also relates to a method of manufacturing abonding tool for bonding a fine wire to a substrate, comprising thesteps of forming a cylindrical body from a non-conductive material;forming a substantially conical body from a conductive material; joiningthe cylindrical body to the conical body; and forming an orificeextending from an end of the cylindrical body to a tip of the conicalbody.

These and other aspects will become apparent in view of the detaileddescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following Figures:

FIG. 1 is a cross sectional view of a conventional bonding tool;

FIGS. 2A-2B are various views of a bonding tool according to a firstexemplary embodiment of the present invention;

FIGS. 3-4 are graphs illustrating energy transition along the length ofthe exemplary bonding tool of the present invention;

FIG. 5 is a graph plotting normalized Y displacement over the length ofthe exemplary bonding tool of the present invention;

FIG. 6A-6I illustrate various working tips that may be provided in theend portion of the exemplary bonding tool according to the presentinvention;

FIG. 7 illustrates a bond formed using a bonding tool tip according toan exemplary embodiment of the present invention;

FIGS. 8A-8C illustrate an exemplary bonding tool tip according to anexemplary embodiment of the present invention;

FIG. 9 illustrates an exemplary bonding tool tip according to anotherexemplary embodiment of the present invention;

FIG. 10 illustrates an exemplary bonding tool tip according to yetanother exemplary embodiment of the present invention; and

FIG. 11 illustrates a second bond formed using the bonding tool tip ofFIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

To overcome the aforementioned deficiencies, the present inventionprovides a multipart capillary (bonding tool) in which the shaft isformed separately from the working tip and subsequently attachedthereto. The present invention also provides a multipart capillary(bonding tool) in which the shaft is formed from a non-conductivematerial and the conical tip is formed from a conductive materialcapable of being machined with the desired features.

FIG. 2A is a side view of a bonding tool according to a first exemplaryembodiment of the present invention. As shown in FIG. 2A, bonding tool202 is coupled to ultrasonic bond head 200 of a bonding machine (notshown). Bonding tool 202 is comprised of shaft portion 204, formed froma non-conductive material, such as alumina, and a conical portion 206having a tip portion 210. Conical portion 206 and tip portion 210 formedfrom a material having a conductive property, such as a metallic basedmaterial, and preferably formed as a unitary part. The shaft portion 204and conical portion 206 are joined to one another at interface 208 usingany one of a variety of well-known means, such as an adhesive, brazing,heat and pressure, or threads for example. Conical portion 206 and tipportion 210, being formed from a metallic based material, allows it tobe machined easily to incorporate features necessary to form bondsuseful in various bonding applications, including ultra-fine pitchbonding. Metals, being malleable, also have certain resistance tocracking and breakage as compared to brittle materials, such as ceramicsand, as such, are ideal in forming bonding tips with ultra-fine pitchfeatures. An additional advantage is that conical portion 206 may bereplaced as it wears out and reusing shaft portion 204 if desired.

FIG. 2B is a perspective view of the parts used to form bonding tool202. As shown in FIG. 2B, shaft (shank) portion 204 is formed from awell-known ceramic, such as alumina. Conical portion 206 and tip portion210 are formed from any one of a number of materials having conductiveproperties, such as Titanium carbide (TiC), TiC based cermet, TiCN, TiNin combination with Si3N4, and Piezo-electric crystals, for example. Themachining of shaft 204, conical portion 206 and tip portion 210 may beaccomplished using conventional means, such as direct die pressingfollowed by sintering or injection molding followed by sintering. Theseparts may then be machined to final shape by grinding or ElectroDischarge Machining operations (EDM), for example.

FIG. 3 is a graph illustrating the displacement magnitude along thelength of bonding tool 202. Curve 300 illustrates a conventional unitarypiece bonding tool while curve 302 illustrates a bonding tool accordingto an exemplary embodiment of the present invention. As shown in FIG. 3,at point 208 there is a smooth transition where conical portion 206 iscoupled to shaft 204.

FIGS. 4 and 5 are other graphs illustrating the displacement magnitudealong the length of bonding tool 202 for various material combinations.As illustrated in FIG. 4, point 400 is where shaft 204 of bonding tool202 is coupled to an ultrasonic transducer (not shown) and point 402(point 502 in FIG. 5) is where conical portion 206 is coupled to shaftportion 204. Once again, the transition between the shaft 204 and theconical portion 206 is smooth.

As discussed above, to enable ultra-fine pitch bonding where a highdegree of inter metallic coverage (IMC) may be achieved, it is necessaryto machine the tip portion 210 of bonding tool 202 to meet theparticular application. The inventors have determined that certain tipfeatures provide significant IMC in an ultra-fine pitch application.Several of these tip configurations are illustrated in FIGS. 6A-6I and8-10. For example, tip portion 210 may have a substantially roundchamfer, a substantially round chamfer with at least one groovetraversing the round chamfer, a substantially round chamfer incombination with a micro-pitch tip, a substantially square chamfer, asubstantially rectangular chamfer, and other geometric shaped chamfers.In one exemplary embodiment, side cuts are formed in conical portion 206and adjacent the chamfered region of tip portion 210. These various tipfeatures are now able to be formed because of the metallic basedcomposition of the conical portion 206/tip portion 210.

FIGS. 6B-6I illustrate plan views, perspective views and sectional viewsof selected ones of the aforementioned examples. With respect todimension of these features, the inventors have discovered that toensure adequate IMC the following relationship is important:If CDx<or=CDy then CDh=((CDx−H)/2)* tan (ICA/2)If CDx>CDy then CDh=((CDy−H)/2)* tan (ICA/2)

Referring now to FIGS. 8A-8C, a portion of tip portion 810 according toan exemplary embodiment of the present invention is illustrated in anupward facing orientation; that is, the bottom portion of tip 810 isfacing upward on the page. As shown in FIG. 8A, tip portion 810 has afrustum conical shape with an outer radius (OR) 812 at a bottom portionthereof. A range for radius 812 is between 2 microns and 50 microns.Adjacent an end of outer radius 812 is outer planar portion 814 whichextends toward and is coupled to one end of arcuate inner chamfer 818.In turn, the other end of inner chamfer 818 is coupled to the lowerportion of longitudinally extending orifice 822 having a diameter ØH.Inner chamfer 818 has a radius ICr of between about 3 and 30 microns andforms inner chamfer area 816 having an chamfer diameter (CD) measuredacross the face of tip portion 810 of between about ØH+(3-15) microns.Outer planar potion 814 is set at an angle, known as the face angle (FA)828 of the bonding tool tip, of between about 0 and 15 degrees.

Referring now to FIG. 8B, a cross sectional view of FIG. 8A taken atsection lines B-B is illustrated. As shown in FIG. 8B, and in greaterdetail in FIG. 8C, inner chamfer 818 has a radius ICr and a height ICh.As can be appreciated by those skilled in the art, by providing an innerchamber with a radius a greater mass of bonding material is presented tothe bonding site (not shown). Ranges for ICr and ICh are between about 3and 30, and 3 and 10, respectively.

Referring now to FIGS. 9A-9C, a portion of tip portion 910 according toanother exemplary embodiment of the present invention is illustrated. Asshown in FIG. 9A, tip portion 910 also has a frustum conical shape withan outer radius (OR) 912 at a bottom portion thereof. A range for OR 912is between 2 microns and 50 microns. Adjacent an end of outer radius 912is outer planar portion 914 which extends toward and is coupled to oneend of planar inner chamfer 918. In turn, the other end of planar innerchamfer 918 is coupled to the lower portion of longitudinally extendingorifice 922. Inner chamfer 918 forms inner chamfer area 916. Planarpotion 914 is set at an angle known as the face angle (FA) 928 of thebonding tool tip of between about 0 and 15 degrees.

Referring now to FIG. 9B, a cross sectional view of FIG. 9A taken atsection lines B-B is illustrated. As shown in FIG. 9B, and in greaterdetail in FIG. 9C, inner chamfer area 916 has a substantiallyrectangular or square profile, when viewed on end, with an inner chamferangle ICA of between about 30 and 120 degrees. By providing an innerchamber with a rectangular or square profile, the bonding tool is betterable to utilize most if not all of the surface of a rectangular orsquare boning pad. This is marked contrast to a circular bond placed ora square or rectangular pad. This is illustrated in FIG. 7.

FIG. 7 is a perspective view illustrating the greater utilization of thesurface area of bond pad 1106 with a like shaped bond 1104 formed bybonding tool tip 910. The difference is easily determined from acomparison of the area of a circle versus the area of a square assumingthat the diameter of the circle is equal to the length of a side of thesquare as follows:(Π/4)L²<L²

Assuming that L=D, where L=length of side; D=diameter of circle, the useof a square bond yields about a 27% increase in surface area over thatof a conventional circular bond.

Referring again to FIGS. 9A-9C, in one exemplary embodiment, a planararea 920 may be formed along opposite portions of tip 920. This providesclearance between bonds for ultra-fine pitch applications. Althoughillustrated as part of a square bond embodiment, the invention is not solimited. It is also contemplated that planar portions 920 may be usedwith bonding tool tips that form other bond profiles, such as round,rectangular, etc.

Referring now to FIGS. 10A-10C, a portion of tip portion 1010 accordingto another exemplary embodiment of the present invention is illustrated.As shown in FIG. 10A, tip portion 1010 has a frustum conical shape witha concave or inverted outer radius (OR) portion 1012 at a bottom portionthereof. A range for the radius of portion 1012 is between 2 microns and30 microns. Adjacent an end of inverted outer radius portion 1012 isouter planar portion 1014 which extends toward and is coupled to one endof inner chamfer 1018. The point at which outer radius portion 1012 iscoupled to outer planar portion 1014 forms an edge 1026 having an angleof between 0 and 15 degrees. In turn, the other end of inner chamfer1018 is coupled to the lower portion of longitudinally extending orifice1022. Inner chamfer 1018 forms inner chamfer area 1016. Outer planarportion 1014 has a face angle (FA) 1028 of between about 0 and 15degrees. In one exemplary embodiment, inner chamfer 1018 has an arcuateprofile. The invention is not so limited, however, in that it iscontemplated that inner chamfer may have other profiles, such as theplanar profile described above with respect to FIG. 9, or otherconventional profiles.

Referring now to FIGS. 10B-10C, a cross sectional view of FIG. 10A takenat section lines B-B, and a plan view are illustrated, respectively. Anadvantage of this embodiment that edge 1026 improves the 2^(nd) bond,typically a wedge bond, formed by bonding tip 1010, over conventionalbonding tools.

FIG. 11 is a side view illustrating an improved 2^(nd) bond 1110 formedby tip portion 1010 on bonding wire 1100. The difference in the 2^(nd)bond 1110 (shown as solid lines including portion 1112) is easily seenin comparison to a 2^(nd) bond formed by a conventional bonding tool(illustrated as dashed lines 1114). The inventors have found that byusing an outer radius 1012 with a concave profile provides additionalmaterial (the material between solid line 1112 and dashed line 1114) forthe 2^(nd) bond, thus improving the adhesive property of the 2^(nd) bondto a bonding site (not shown).

Although the invention has been described with reference to exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed to include other variants and embodiments of theinvention which may be made by those skilled in the art withoutdeparting from the true spirit and scope of the present invention.

1. A bonding tool for bonding a wire to a substrate comprising: a bodyportion formed from a first material; and a working tip formed from asecond material, a first end of the working tip coupled to one end ofthe body portion.
 2. The bonding tool according to claim 1, wherein thefirst material and the second material are similar materials.
 3. Thebonding tool according to claim 1, wherein first material is a firstnon-conductive material and the second material is a secondnon-conductive material.
 4. The bonding tool according to claim 1,wherein first material is a non-conductive material and the secondmaterial is a conductive material.
 5. A bonding tool for bonding a wireto a substrate comprising: a body portion formed from a firstnon-conductive material; and a working tip formed from a second materialhaving a conductive property, a first end of the working tip coupled toone end of the body portion, the second material being different thanthe first material.
 6. The bonding tool according to claim 5, wherein asecond end of the working tip has a face with an inner chamferedportion.
 7. The bonding tool according to claim 6, wherein the innerchamfered portion has a substantially circular profile.
 8. The bondingtool according to claim 6, wherein the inner chamfered portion has asubstantially square profile.
 9. The bonding tool according to claim 6,wherein the inner chamfered portion has a substantially rectangularprofile.
 10. The bonding tool according to claim 5, further comprising aplanar portion formed in the working tip and adjacent the innerchamfered portion.
 11. The bonding tool according to claim 10, whereinthe planar portion includes at least two substantially parallel faceportions.
 12. The bonding tool according to claim 5, wherein working tiphas a substantially conical profile.
 13. A bonding tool for bonding awire to a substrate comprising: a body portion formed from a firstnon-conductive material; and a working tip formed from a second materialhaving a conductive property, a first end of the working tip coupled toone end of the body portion, the working tip comprising: i) an orificeextending in a longitudinal direction along a central portion of theworking tip, ii) an inner chamfer coupled to an end of the orifice, theinner chamfer having a substantially arcuate profile, and iii) aexterior planar portion coupled to an end of the inner chamfer.
 14. Thebonding tool according to claim 13, wherein the bonding tool forms bondshaving at least a partially arcuate profile extending from a bottomportion of the bond toward an upper portion of the bond.
 15. A workingtip of a bonding tool for use with a bonding machine, the working tipcomprising: an orifice extending in a longitudinal direction along acentral portion of the working tip; an inner chamfer coupled to an endof the orifice, the inner chamfer having a substantially arcuateprofile; and a exterior planar portion coupled to an end of the innerchamfer.
 16. The working tip according to claim 15, wherein the innerchamfer has an interior radius of between about 5 microns and 30microns.
 17. The working tip according to claim 16, wherein the innerchamfer has a diameter of between about ØH+3 microns and ØH+15 micronsas measured at a junction between the inner chamfer and the exteriorplanar portion, where ØH is the diameter of the orifice.
 18. The workingtip according to claim 16, wherein the exterior planar portion of theworking tip has an angle of between about 0 and 15 degrees.
 19. Theworking tip according to claim 15, further comprising an arcuate portionextending between an end of the planar portion and a side surface of theworking tip, the arcuate portion having a radius of between about 2 and50 microns.
 20. A working tip of a bonding tool for use with a bondingmachine, the working tip comprising: an orifice extending in alongitudinal direction along a central portion of the working tip; aplurality of substantially planar faces formed at an inner portion ofthe working tip to form an inner chamfer having a polygonal shape; and aexterior planar portion coupled to respective ends of each of pluralityof substantially planar faces.
 21. The working tip according to claim20, wherein each of the plurality of substantially planar faces arecoupled to one another on adjacent sides, and each of plurality ofsubstantially planar faces are coupled to an end of the orifice.
 22. Theworking tip according to claim 20, further comprising an arcuate portionextending between an end of the exterior planar portion and a sidesurface of the working tip, the arcuate portion having a radius ofbetween about 2 and 50 microns.
 23. The working tip according to claim22, further comprising a plurality planar portions formed on at least aportion of the side surface of the working tip, at least two of theplurality of planar portions substantially parallel to one another. 24.The working tip according to claim 20, wherein the inner chamfer has asquare shape.
 25. The working tip according to claim 20, wherein theinner chamfer has a rectangular shape.
 26. The working tip according toclaim 20, wherein the working tip forms bonds having a plurality ofsubstantially planar exterior faces coupled to one another at adjacentedges and extending from a bottom portion of the bond toward an upperportion of the bond.
 27. A working tip of a bonding tool for use with abonding machine, the working tip comprising: an orifice extending in alongitudinal direction along a central portion of the working tip; aninner chamfer having a first end coupled to an end of the orifice; aexterior planar portion having a first end coupled to a second end ofthe inner chamfer; and a further exterior portion coupled to a secondend of the exterior planar portion, the further exterior portiondisposed coaxially with the orifice and having a portion with a concaveprofile extending from the exterior planar portion.
 28. The working tipaccording to claim 27, wherein the inner chamfer has a substantiallyarcuate profile.
 29. The working tip according to claim 27, wherein theinner chamfer has a substantially concave profile.
 30. The working tipaccording to claim 27, wherein the inner chamfer has a substantiallyplanar profile.
 31. A method of manufacturing a capillary bonding toolfor bonding a fine wire to a substrate, the method comprising the stepsof: forming a cylindrical body from a non-conductive material; forming asubstantially conical body from a conductive material; joining thecylindrical body to the conical body; and forming an orifice extendingfrom an end of the cylindrical body to a tip of the conical body. 32.The method according to claim 31, wherein the orifice may be formedindependently in each of the cylindrical body and the conical body. 33.The method according to claim 31, further comprising the step of:forming a substantially rectangular chamfered portion in a face of theworking tip.
 34. The method according to claim 31, further comprisingthe step of: forming at least one groove along at least a portion of aface of the working tip, the groove coupled to an end of the orifice.35. A method of manufacturing a working tip for a capillary bonding toolfor bonding a fine wire to a substrate, the method comprising the stepsof: forming an orifice extending in a longitudinal direction along acentral portion of the working tip; forming a circumferential innerchamfer having a substantially arcuate cross section at an end of theorifice; and forming a circumferential planar portion on an exteriorsurface of the working tip, an innermost end of the circumferentialplanar portion coupled to an end of the circumferential inner chamfer.36. The method of claim 35, wherein the inner chamfer forming stepprovides an interior radius of between about 3 microns and 30 microns.37. A method of manufacturing a working tip for a capillary bonding toolfor bonding a fine wire to a substrate, the method comprising the stepsof: forming an orifice extending in a longitudinal direction along acentral portion of the working tip; forming a plurality of substantiallyplanar faces at an inner portion of the working tip to form an innerchamfer having a polygonal shape; and forming a circumferential planarportion on an exterior surface of the working tip, an innermost portionof the circumferential planar portion coupled to an end of the innerchamfer.
 38. A method of manufacturing a working tip for a capillarybonding tool for bonding a fine wire to a substrate, the methodcomprising the steps of: forming an orifice extending in a longitudinaldirection along a central portion of the working tip; forming an innerchamfer at an end of the orifice; forming a circumferential planarportion on an exterior surface of the working tip, an innermost end ofthe circumferential planar portion coupled to an end of the innerchamfer; and forming a further circumferential exterior adjacent asecond end of the exterior planar portion, the further exterior portionhaving a concave profile in cross section.